1. Field of the Invention
This invention relates to a coupling for establishing a releasable torque transmitting connection between a hollow shaft element and a journal element co-axially positioned therein, by means of coupling members provided in apertures in the hollow shaft element and radially movable therein to be engagable, when in radially inner positions, with respective recesses in the journal element for torque transmission with the shaft element, and an operating sleeve movable axially on the shaft element and having an annular operating face engagable with said coupling members for effecting radial inward movement thereof and a retaining face engagable with the coupling members to hold them in their radially inner positions.
Releasable torque transmitting couplings of the kind above set forth may be used in the drive line of four-wheel drive vehicles, wherein one axle, either the front or rear wheels of the vehicle, is permanently driven while the other axle is either engaged only under particular operating conditions, e.g. in the case of bad traction and slip of the wheels of the permanently driven axle, or wherein drive to the second axle is disengaged under certain operating conditions, e.g. when braking to ensure vehicle stability and accurate functioning of an anti-lock braking system if such is provided.
2. Description of the Prior Art
Various forms of releasable torque transmitting coupling are known, e.g. the one described in DE-3822115A which may be described as a claw coupling mechanism. However, such a coupling is hardly suitable for disconnecting the drive when torque is transmitted, and reconnecting it if there is a high speed difference between the elements to be coupled. Locking the axially displaceable claw sleeve is effected by way of radially displaceable locking members in the form of balls, which engage a groove in the respective hollow shaft where they are radially fixed by a locking sleeve, to axially secure the claw sleeve. Otherwise the latter might be axially displaced by the reaction forces of the teeth.
Couplings operable to be connected or released whilst under load are known from other fields of application, e.g. from JP 60-256627. In this coupling, locking members are radially displaceably held in apertures of a driving gear sleeve, freely rotating on a shaft, and engage individual recesses or grooves on the shaft where, while connecting the driving gear sleeve to the shaft, they are held by an axially displaceable locking sleeve. The locking sleeve is displaced axially by an operating fork which is magnetically actuated through a suitable lever mechanism.